The present invention relates to planar filters having periodic electromagnetic bandgap (EBG) substrates.
An EBG substrate, which is coated with metal on both sides creating a parallel plate, is either periodically loaded with metal or dielectric rods. For metallic inclusions, the substrate is loaded with metallic rods, effectively creating a high pass, two-dimensional filter that blocks energy from propagating in the substrate from DC to an upper cutoff. This form of arrangement is termed a metallo-dielectric EBG (also termed Photonic Bandgap or PBG). For dielectric inclusions, a two-dimensional band stop effect is created within the periodic material. This form of periodic substrate is termed a two-dimensional dielectric EBG.
An EBG defect resonator is made by intentionally interrupting the otherwise periodic lattice. The defect localizes energy within the lattice, and a resonance is created. A single defect resonator has been shown to provide high Qs, which make this resonator a good candidate for a sharp bandwidth, low insertion loss filter.
Using the concept of a constant coupling coefficient filter, a defect resonator is used to develop multipole filters. These filters exhibit excellent insertion loss and isolation due to the high Q exhibited by the Electromagnetic Bandgap (EBG) defect resonators. The fabrication of these filters requires nothing more than simple via apertures on a single substrate plane. In addition, the planar nature of these filters makes the filters amenable to 3-D circuit applications. Finally, since the EBG substrate prohibits substrate modes, the isolation between the input and output ports of the filter can be much greater than that of other planar architectures. Two, three, and six pole 2.7% filters were measured and simulated, with measured results showing insertion losses of xe2x88x921.23, xe2x88x921.55, and xe2x88x923.28 dB, respectively. The out-of-band isolation was measured to be xe2x88x9232, xe2x88x9246, and xe2x88x9282 dB at 650 MHZ away from the center frequency (6% off center) for the three filters.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.